Liquid-crystalline polymer composition and molded article thereof

ABSTRACT

A liquid-crystalline polymer composition containing a liquid-crystalline polymer and a magnetic filler formed by heat-treating a composite material of a ceramic powder and a soft magnetic metal powder in an inert gas atmosphere.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid-crystalline polymercomposition having an electromagnetic shielding property and an electricinsulation property, and to a molded article thereof.

2. Related Background Art

Recently, according to the trend toward higher performance of electricand electronic equipment, for example, telecommunications equipment suchas a portable telephone, and office automation (OA) apparatuses such aspersonal computer, the operating frequency thereof has become higherfrequency. On the other hand, since electric and electronic equipmentworking at an operating frequency in high frequencies has electric andelectronic components such as a processor and a communication cableeasily radiating electromagnetic waves of high frequency, there is aproblem that malfunction may easily occur due to the electromagneticwaves. Furthermore, the electromagnetic wave may cause malfunction inneighboring other electric and electronic equipment, and there is aconcern that the electromagnetic wave may affect human bodies.Therefore, electric and electronic components easily radiatingelectromagnetic waves of high frequency are provided with an enclosuremade of electromagnetic shielding materials.

The electromagnetic shielding materials include insulating materialsattenuating electromagnetic waves by absorption and conductive materialsreflecting electromagnetic waves, but the former materials arepreferable from the viewpoint of preventing malfunction of electric andelectronic equipment due to reflected electromagnetic waves. Thus, asthe electromagnetic shielding materials, insulating resin compositionscontaining a resin and a magnetic filler are investigated, and amongthem, a liquid-crystalline polymer composition containing aliquid-crystalline polymer and a magnetic filler is preferablyinvestigated because the liquid-crystalline polymer composition hasexcellent melting fluidity, is easily molded, and has high heatresistance and mechanical strength. For example, Japanese PatentApplication Laid-Open Publication No. 2001-237591 discloses aliquid-crystalline polymer composition containing a liquid-crystallinepolymer and a coupling-treated soft magnetic powder.

SUMMARY OF THE INVENTION

However, a conventional liquid-crystalline polymer compositioncontaining a liquid-crystalline polymer and a magnetic filler is notnecessarily sufficient in an electromagnetic shielding property and aninsulating property. Furthermore, in molding of a liquid-crystallinepolymer composition, it is advantageous in terms of the operability thatthe liquid-crystalline polymer composition is granulated into pellets inadvance, and the pellets are molded, but in a conventionalliquid-crystalline polymer composition containing a liquid-crystallinepolymer and a magnetic filler, a strand is easily cut at the time ofgranulation, thus making the granulation difficult. Then, an object ofthe present invention is to provide a liquid-crystalline polymercomposition containing a liquid-crystalline polymer and a magneticfiller, having excellent electromagnetic shielding property andinsulating property, and being easily granulated.

In order to achieve the above object, the present invention provides aliquid-crystalline polymer composition containing a liquid-crystallinepolymer and a magnetic filler obtained by heat-treating a compositematerial containing a ceramic powder and a soft magnetic metal powder inan inert gas atmosphere. Furthermore, the present invention alsoprovides a molded article formed by molding this liquid-crystallinepolymer composition.

Since the liquid-crystalline polymer composition of the presentinvention has excellent electromagnetic shielding property andinsulating property and is easily granulated, a molded article havingexcellent electromagnetic shielding property and insulating property canbe advantageously produced by molding the liquid-crystalline polymercomposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A liquid-crystalline polymer used in the present invention is a polymershowing an optical anisotropy at the time of melting and forming ananisotropic melt at a temperature of 450° C. or less. The opticalanisotropy can be confirmed by a usual polarization examination methodusing an orthogonal polarizer. The liquid-crystalline polymer has a longnarrow and flat molecular shape and has a molecular chain having highrigidity, that is, a so-called mesogenic group, along the long chain ofthe molecule, in which either or both of a polymer main chain and a sidechain may contain such a mesogenic group, but when the resultant moldedarticle is required to have higher heat resistance, it is preferablethat the polymer main chain has the mesogenic group.

Examples of the liquid-crystalline polymer include liquid-crystallinepolyesters, liquid-crystalline polyesteramides, liquid-crystallinepolyesterethers, liquid-crystalline polyester carbonates,liquid-crystalline polyesterimides, liquid-crystalline polyamides, andthe like; among them, liquid-crystalline polyesters, liquid-crystallinepolyesteramides, and liquid-crystalline polyamides are preferablebecause a molded article having more excellent strength is obtained;liquid-crystalline polyesters and liquid-crystalline polyesteramides arepreferable because a less water-absorptive molded article is obtained;and fully aromatic liquid-crystalline polyesters are particularlypreferable.

Preferable examples of the liquid-crystalline polymer includeliquid-crystalline polyesters shown in the below-mentioned (A1) to (A8),and two or more of them can be used in combination if necessary.

(A1): Liquid-crystalline polyesters having a repeating unit representedby formula (i).

(A2): Liquid-crystalline polyesters having a repeating unit representedby formula (ii) and a repeating unit represented by formula (iii).

(A3): Liquid-crystalline polyesters having the repeating unitrepresented by formula (i), the repeating unit represented by formula(ii) and the repeating unit represented by formula (iii).

(A4): Liquid-crystalline polyesteramides or liquid-crystallinepolyamides in which a part or all of the repeating unit represented byformula (i) is replaced by a repeating unit represented by formula (iv)in the (A1).

(A5): Liquid-crystalline polyesteramides or liquid-crystallinepolyamides in which a part or all of the repeating unit represented byformula (iii) is replaced by a repeating unit represented by formula (v)and/or a repeating unit represented by formula (vi) in the (A2).

(A6): Liquid-crystalline polyesteramides in which a part or all of therepeating unit represented by formula (i) is replaced by the repeatingunit represented by formula (iv) in the (A3).

(A7): Liquid-crystalline polyesteramides in which a part or all of therepeating unit represented by formula (iii) is replaced by the repeatingunit represented by formula (v) and/or the repeating unit represented byformula (vi) in the (A3).

(A8): Liquid-crystalline polyesteramides or liquid-crystallinepolyamides in which a part or all of the repeating unit represented byformula (i) is replaced by the repeating unit represented by formula(iv), and a part or all of the repeating unit represented by formula(iii) is replaced by the repeating unit represented by formula (v)and/or the repeating unit represented by formula (vi) in the (A3).

—O—Ar¹—CO—  (i)

—CO—Ar²—CO—  (ii)

—O—Ar³—O—  (iii)

—NH—Ar⁴—CO—  (iv)

—O—Ar⁵—NH—  (v)

—NH—Ar⁶—NH—  (vi)

(In the formulae, Ar¹ and Ar⁴ each independently represent a1,4-phenylene group, a 2,6-naphthalenediyl group or a 4,4′-biphenylylenegroup. Ar², Ar³, Ar⁵ and Ar⁶ each independently represent a1,4-phenylene group, a 2,6-naphthalenediyl group, a 1,3-phenylene groupor a 4,4′-biphenylylene group. Furthermore, a hydrogen atom present inthe group represented by Ar¹, Ar², Ar³, Ar⁴, Ar⁵ or Ar⁶ may eachindependently be replaced by a halogen atom, an alkyl group or an arylgroup.)

The repeating unit (i) is a repeating unit derived from an aromatichydroxy carboxylic acid. Examples of the aromatic hydroxy carboxylicacid include 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid,4′-hydroxy biphenyl-4-carboxylic acid, and aromatic hydroxy carboxylicacids in which a part or all of hydrogen atoms on the aromatic ringpresent in these aromatic hydroxy carboxylic acids are replaced by analkyl group, an aryl group or a halogen atom.

The repeating unit (ii) is a repeating unit derived from an aromaticdicarboxylic acid. Examples of the aromatic dicarboxylic acid includeterephthalic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid,4,4′-diphenyl dicarboxylic acid, and aromatic dicarboxylic acids inwhich a part or all of hydrogen atoms on the aromatic ring present inthese aromatic dicarboxylic acids are replaced by an alkyl group, anaryl group or a halogen atom.

The repeating unit (iii) is a repeating unit derived from an aromaticdiol. Examples of the aromatic diol include hydroquinone,naphthalene-2,6-diol, resorcin, 4,4′-biphenylenediol, and aromatic diolsin which a part or all of hydrogen atoms on the aromatic ring present inthese aromatic diols are replaced by an alkyl group, an aryl group or ahalogen atom.

The repeating unit (iv) is a repeating unit derived from an aromaticaminocarboxylic acid. Examples of the aromatic aminocarboxylic acidinclude 4-aminobenzoic acid, 6-amino-2-naphthoic acid, 4′-aminobiphenyl-4-carboxylic acid, and aromatic aminocarboxylic acids in whicha part or all of hydrogen atoms on the aromatic ring present in thesearomatic aminocarboxylic acids are replaced by an alkyl group, an arylgroup or a halogen atom.

The repeating unit (v) is a repeating unit derived from an aromaticamine having a hydroxyl group. Examples of the aromatic amine having ahydroxyl group include 4-amino phenol, 6-amino-2-naphthol, 3-aminophenol, 4-amino-4′-hydroxy diphenyl, and aromatic hydroxy amines inwhich a part or all of hydrogen atoms on the aromatic ring present inthese aromatic amines having a hydroxyl group are replaced by an alkylgroup, an aryl group or a halogen atom.

The repeating unit (vi) is a repeating unit derived from an aromaticdiamine. Examples of the aromatic diamine include 1,4-phenylenediamine,2,6-naphthalene diamine, 1,3-phenylenediamine, 4,4′-biphenylylenediamine, and aromatic diamines in which a part or all of hydrogen atomson the aromatic ring present in these aromatic diamines are replaced byan alkyl group, an aryl group or a halogen atom.

Examples of substituents that the repeating units (i) to (vi) have,include as an alkyl group a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, a tert-butyl group, a hexylgroup, a cyclohexyl group, an octyl group, and a decyl group, and thealkyl group has usually 1 to 10 carbon atoms, may be linear or branched,or may be alicyclic. Furthermore, examples of the aryl group include aphenyl group, and a naphthyl group, and the aryl group has usually 6 to10 carbon atoms. Furthermore, examples of the halogen atom include afluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

In the above-mentioned liquid-crystalline polymers, theliquid-crystalline polyester selected from the group consisting of (A1)to (A3) is preferable from the viewpoint of obtaining a molded articlehaving more excellent heat resistance and dimension stability; theliquid-crystalline polyester of (A1) or (A3) is more preferable; and theliquid-crystalline polyester of (A3) is further preferable.

As mentioned above, the liquid-crystalline polyester of (A1) has arepeating unit (i), and preferably has a plurality of types of repeatingunits (i). The reason therefor is because it has an excellent balancebetween the heat resistance and the molding processing property.

The liquid-crystalline polyester of (A3) has the repeating unit (i), therepeating unit (ii) and the repeating unit (iii), and when the totalthereof is 100 mol %, it is preferable that the content of the repeatingunit (i) is 30 to 80 mol %, the content of the repeating unit (ii) is 10to 35 mol %, and the content of the repeating unit (iii) is 10 to 35 mol%. Note here that the molar ratio of the repeating unit (ii) to therepeating unit (iii), when represented by the repeating unit (ii)/therepeating unit (iii), is preferably 0.9/1.0 to 1.0/0.9, and it isadvantageous that the ratio is 1.0/1.0, that is, substantially theequimolar ratio, because, in producing a liquid-crystalline polyester,the numbers of carboxyl groups and hydroxyl groups, capable of formingan ester bond are the same, so that the molecular weight of theresultant liquid-crystalline polyester can be increased, and thus amolded article having more excellent heat resistance can be obtained.

Herein, when the content of the repeating unit (i) is too small and thecontent of the repeating unit (ii) and/or the repeating unit (iii) istoo large, it tends to be difficult for the obtained polyester toexhibit the liquid-crystalline property. On the other hand, when thecontent of the repeating unit (i) is too large and the content of therepeating unit (ii) and/or the repeating unit (iii) is too small, it isdifficult for the obtained liquid-crystalline polyester to be melted,and thus the moldability tends to be deteriorated.

The content of the repeating unit (i) is more preferably 40 to 70 mol %,and further preferably 45 to 65 mol %. Furthermore, the contents of therepeating unit (ii) and the repeating unit (iii) are more preferably 15to 30 mol % respectively, and further preferably 17.5 to 27.5 mol %,respectively.

The liquid-crystalline polyester of (A1) or (A3) can be obtained bypolymerizing a raw material monomer deriving the liquid-crystallinepolyester, that is, a plurality of types of aromatic hydroxy carboxylicacids, or aromatic hydroxy carboxylic acid, aromatic dicarboxylic acidand aromatic diol by well-known means. Among them, in the aspect of theease in producing a liquid-crystalline polyester, it is preferable thata raw material monomer is previously converted into an ester-formingderivative, followed by producing a liquid-crystalline polyester.

Herein, the ester-forming derivatives are derivatives having a group forpromoting an ester formation reaction, and in the case of a raw materialmonomer having a carboxyl group in the molecule, examples of theester-forming derivatives include a derivative in which the carboxylgroup is converted into a haloformyl group or an acyloxycarbonyl group,and a derivative in which the carboxyl group is converted into analkoxycarbonyl group with lower alcohol. Furthermore, in the case of araw material monomer having a hydroxyl group in the molecule, examplesof the ester-forming derivatives include a derivative in which thehydroxyl group is converted into an acyloxy group with a lowercarboxylic acid.

A particularly preferable method of producing a liquid-crystallinepolyester using such ester-forming derivatives is a method usingester-forming derivatives in which a hydroxyl group of an aromatichydroxy carboxylic acid and an aromatic diol is converted into anacyloxy group with a lower carboxylic acid. This acylation is usuallycarried out by allowing a compound having a hydroxyl group to react withacetic anhydride. A liquid-crystalline polyester can be obtained bysubjecting such a ester-forming derivative to deacetation polymerizationwith an aromatic dicarboxylic acid.

Examples of the method of producing a liquid-crystalline polyester usingthe ester-forming derivative may include a method described in JapanesePatent Application Laid-Open Publication No. S61-69866 as a method ofproducing the liquid-crystalline polyester of (A1), and a methoddescribed in Japanese Patent Application Laid-Open Publication No.2002-146003 as a method of producing the liquid-crystalline polyester of(A3). That is to say, monomers corresponding to the repeating unit (i),the repeating unit (ii) and the repeating unit (iii) are mixed with eachother and acylated with acetic anhydride so as to form ester-formingderivatives, then a raw material monomer containing the ester-formingderivatives is melt-polymerized, and thus the liquid-crystallinepolyester can be obtained.

Herein, when a molded article having more excellent heat resistance isintended, it is preferable that the liquid-crystalline polyesterobtained by the melt polymerization is used as a prepolymer and themolecular weight of the prepolymer is further increased, and it isadvantageous that such increasing of the molecular weight of theprepolymer is carried out by employing solid phase polymerization. Thissolid phase polymerization can be carried out by pulverizing theprepolymer into powder and heating the powder. With this solid phasepolymerization, polymerization further proceeds, so that a highermolecular weight can be achieved.

When the prepolymer is made into powder, for example, the prepolymer maybe pulverized after it is cooled and solidified. The average particlesize of the powder obtained by pulverizing is preferably 0.05 to 3 mm,and more preferably 0.05 to 1.5 mm because an increase in the molecularweight of the liquid-crystalline polyester is further promoted. It isfurthermore preferable that the average particle size is 0.1 to 1.0 mmbecause sintering between particles does not occur, so that theoperability of the solid phase polymerization tends to be improved, andthus the molecular weight of the liquid crystal polyester is efficientlyincreased. Note here that the average particle size of the prepolymercan be determined by external observation and the like.

In the preferable solid phase polymerization, firstly, the temperatureis raised from room temperature to a temperature at least 20° C. lowerthan the flow starting temperature of the prepolymer. The temperaturerising time at this time is preferably within 1 hour from the viewpointof reducing the reaction time. Next, the temperature is raised from thetemperature at least 20° C. lower than the flow starting temperature ofthe prepolymer to a temperature of 280° C. or higher. The temperature israised preferably at a temperature-rising rate of 0.3° C./min or less,and more preferably at 0.1 to 0.15° C./min. The temperature-rising rateof 0.3° C./min or less makes it difficult for the sintering betweenparticles of the powder to occur, and thus, makes it possible to produceliquid-crystalline polyester having a higher molecular weight.

Furthermore, in order to increase the molecular weight of theliquid-crystalline polyester, it is preferable that the reaction iscarried out usually at 280° C. or higher, and preferably at 280° C. to400° C. for 30 minutes or more in the final process of the solid phasepolymerization. In particular, from the viewpoint of improving the heatstability of a liquid-crystalline polyester, it is preferable that thereaction is carried out at 280° C. to 350° C. for 30 minutes to 30hours, and more preferably at 285° C. to 340° C. for 30 minutes to 20hours. Such heating conditions can be appropriately optimized accordingto the types of raw material monomers used in production of theliquid-crystalline polyester.

The liquid-crystalline polyester of (A3) obtained by carrying out thesolid phase polymerization achieves a sufficiently high molecularweight, so that a molded article having excellent heat resistance can beobtained. The liquid-crystalline polyester has a flow startingtemperature of preferably 250° C. or higher, and more preferably 280° C.to 390° C.

Note here that the flow starting temperature means a temperature atwhich the melt viscosity, measured by using a capillary rheometerequipped with a die having an inner diameter of 1 mm and a length of 10mm when the liquid-crystalline polyester is extruded from a nozzle underthe load of 9.8 MPa (100 kg/cm²) at temperature-rising rate of 4°C./min, is 4800 Pa·s (48,000 poise), and the flow starting temperatureis an index expressing a molecular weight of liquid-crystallinepolyester well known in the art (see, edited by Naoyuki Koide,“Synthesis, Molding, and Application of Liquid-Crystalline Polymer” pp.95-105, CMC Publishing CO., LTD. published Jun. 5, 1987). As a devicefor measuring the flow starting temperature, for example, a flowingproperty evaluation device, “Flow Tester CFT-500D” manufactured byShimadzu Corporation is used.

The liquid-crystalline polyester of (A1) or (A3) is described above as aparticularly preferable liquid-crystalline polymer, but otherliquid-crystalline polymers, for example, the liquid-crystallinepolyesters of (A2), and (A4) to (A8) can be easily produced by theproduction method using the above-mentioned ester-forming derivatives.

The liquid-crystalline polymer composition of the present inventioncontains a liquid-crystalline polymer as mentioned above and a magneticfiller formed by heat-treating a composite material (composite) of aceramic powder and a soft magnetic metal powder in an inert gasatmosphere. Thus, by blending the predetermined magnetic filler with theliquid-crystalline polymer, it is possible to obtain aliquid-crystalline polymer composition having excellent electromagneticshielding property and insulating property and being granulated easily.

The volume average particle size of the magnetic filler is preferably 1to 100 μm, and more preferably 10 to 50 μm from the viewpoint ofdispersibility with respect to a liquid-crystalline polymer.

The soft magnetic metal powder is a powder containing a metal (softmagnetic metal) having a small coercive force and large magneticpermeability, and the magnetic permeability of the soft magnetic metal,when it is represented by relative magnetic permeability divided by themagnetic permeability in vacuum, is preferably 100 or more, and morepreferably 200 or more. Herein, the soft magnetic metal having therelative magnetic permeability of 100 or more can be selected from themetals described in, for example, Chronological Scientific Tables (RIKOHTOSHO) and Noriyuki Nanba and Fumitaka Kaneko “Electricmaterials—Dielectric materials and Magnetic materials—” p. 208 (RIKOHTOSHO, published in March, 1980), and the soft magnetic metal ispreferably cobalt, iron or nickel, and more preferably iron or nickel.

Furthermore, the soft magnetic metal powder may be a powder containingan alloy of soft magnetic metals, and examples of the alloy include anFe—Si alloy (silicon steel), an Fe—Al alloy (alperm), an Fe—Ni alloy(permalloy), an Fe—Co alloy, an Fe—V alloy (Permendur), an Fe—Cr alloy,an Fe—Si alloy (silicon steel), an Fe—Al—Si alloy, an Fe—Cr—Al alloy, anFe—Cu—Nb—Si—B alloy, and an Fe—Ni—Cr alloy referred to as Mu metal, andpreferably, these alloys also have relative magnetic permeability of 100or more.

These soft magnetic metals or alloys thereof can be granulated into asoft magnetic metal powder by using appropriate crusher or classifier.

The soft magnetic metal powder preferably contains iron or an alloythereof as a main component, and the proportion of the iron or the alloythereof in the soft magnetic metal powder is usually 50 to 100 mass %and preferably 80 to 100 mass %. The soft magnetic metals powder havingsuch materials is preferable because they have particularly highrelative magnetic permeability, so that the electromagnetic shieldingproperty of the obtained molded article becomes better. Also, it can besaid that it is advantageous from the viewpoint of cost efficiency.

The aspect ratio of the soft magnetic metal powder is preferably 2 ormore. The aspect ratio herein denotes a value obtained by externallyobserving the soft magnetic metal powder by magnifying them by about 100to 300 times by using a scanning electron microscope or an opticalmicroscope, calculating the ratio (L/S) of the longest diameter (majoraxis L) with respect to the shortest diameter (minor axis S) of eachparticle of about 100 particles, and number-averaging them. It ispreferable that the aspect ratio of the soft magnetic metal powder is 2or more because when the liquid-crystalline polymer composition ismelt-molded, the major axis of the magnetic filler is easily oriented inthe flowing direction (MD), so that when a plane parallel to the MD isdefined as an electromagnetic wave shield plane, the area ratio of themagnetic filler occupied in the plane is easily increased, and theelectromagnetic shielding performance of the magnetic filler can beeffectively used. From this point, the aspect ratio of the soft magneticmetal powder is more preferably 2.5 or more.

It is preferable that the ceramic powder contains silicon oxide as amain component, and it may contain other components, for example,silicon nitride and silicon carbide, and may contain an organic group.The proportion of silicon oxide in the ceramic powder is usually 50 to100 mass %, and preferably 80 to 100 mass %.

As the ceramic powder containing such a silicon oxide as a maincomponent, various substances generally referred to as silica arecommercially available. Such commercially available silica is classifiedinto natural silica and synthetic silica (artificial silica), and thesynthetic silica includes dry synthetic silica and wet synthetic silica.As the natural silica, silica obtained by pulverizing quartz ispreferable because purity of silicon oxide is high; and natural silicaproduced by combining pulverizing and melting quartz is also preferablebecause it has high purity of silicon oxide. Examples of the drysynthetic silica include silica obtained by firing a mixture of silicontetrachloride and hydrogen at about 1000 to 1200° C. in the air, andsilica obtained by melting metal silicon and spraying it into the airvia a nozzle. The dry synthetic silica obtained by such a productionmethod may contain a small amount of a Si—H bond in silica. Ceramicpowder containing such a small amount of a Si—H bond may be used.Furthermore, examples of the wet synthetic silica include silicaobtained by hydrolyzing silicon tetrachloride and alkoxide silicate. Thewet synthetic silica obtained in such a production method may containorganic matters and chlorine as reaction impurities, and may contain asilanol group (Si—OH) in a molecule. Furthermore, such a silanol groupmay be hydrated so that silica contains hydrated water. As the ceramicpowder, such wet synthetic silica can be used, but it is preferable touse wet synthetic silica obtained by treating the above-mentioned wetsynthetic silica at high temperatures of about 800° C. to removehydrated water or organic matters. Such silica is available from, forexample, Admatechs Company Limited, TOSOH SILICA CORPORATION, andpreferably used as raw materials of the above-mentioned compositematerial.

The composite material can be obtained by mixing ceramic powder and softmagnetic metal powder by using a mixer capable of dry-mixing them, forexample, a ball mill, a planetary ball mill, a sand mill and the like.At this time, when a planetary ball mill is used as a mixer, a compositematerial formed by coating a soft magnetic metal powder with a ceramicpowder can be advantageously used, and by using the magnetic fillerobtained from such a composite material, an electric insulation propertyof a molded article obtained from the liquid-crystalline polymercomposition tends to be further preferable. From such a viewpoint, it ispreferable that the ratio of the soft magnetic metal powder and theceramic powder to be used is selected so that the ceramic powder coatsthe soft magnetic metal powder. The mass ratio to be used may beobtained by carrying out the preliminary experiments in several pointsto which the ratios of the soft magnetic metal powder and the ceramicpowder to be used are assigned, observing a cross section of thecomposite material obtained by the preliminary experiment by using, forexample, a scanning electron microscope (SEM), and determining a coatingstate of the ceramic powder. Furthermore, it is preferable that the softmagnetic metal powder and the ceramic powder are mixed in an inert gasatmosphere such as nitrogen and argon in order to prevent the softmagnetic metal powder from being remarkably oxidized.

Furthermore, as the composite material formed by coating soft magneticmetal powder with ceramic powder, composite material, for example, acomposite material formed by coating iron powder with silica particlesis available from Hitachi High-Technologies Corporation. This compositematerial manufactured by Hitachi High-Technologies Corporation isdescribed in the document (Electronic Materials, September 2008).

Note here that in the composite material formed by coating soft magneticmetal powder with ceramic powder, the ceramic powder may coats a part ofthe surface of the soft magnetic metal powder, and it is not necessarilycoats the entire surface of the soft magnetic metal powder.

The magnetic filler is obtained by heat-treating the above-mentionedcomposite material in an inert gas atmosphere such as nitrogen andargon. Herein, the heat-treatment temperature is preferably 800° C. orhigher, and more preferably 900° C. or higher. Furthermore, theheat-treatment time is preferably 5 hours or longer, and more preferably12 hours or longer.

The liquid-crystalline polymer composition of the present invention maycontain components other than the liquid-crystalline polymer and themagnetic filler, if necessary, and examples of such materials includefibrous reinforcing materials such as glass fiber, silica-alumina fiber,alumina fiber, and carbon fiber; needle-like reinforcing materials suchas aluminum borate whisker and potassium titanate whisker; inorganicfillers such as glass beads, talc, mica, graphite, wollastonite, anddolomite; mold release improving agents such as a fluorocarbon resin,and metallic soap; coloring agents such as dyestuffs and pigments;antioxidants; thermal stabilizers; ultraviolet absorbers; surfactants,and the like, and two or more thereof may be used together if necessary.Furthermore, additives having an outer lubricant effect such as higherfatty acids, higher fatty acid esters, higher fatty acid metal salts,and fluorocarbon surfactants can be used. In addition, a small amount ofa thermoplastic resin other than the liquid-crystalline polymer, forexample, polyamide, crystalline polyester, polyphenylene sulfide,polyether ketone, polycarbonate, polyphenylene ether and a denaturedproduct thereof, polysulfone, polyethersulfon, polyetherimide, and thelike; and a thermosetting resin, for example, a phenol resin, and anepoxy resin may be contained.

In the liquid-crystalline polymer composition of the present invention,the content of the magnetic filler is preferably equal to or higher thanthe mass of the liquid-crystalline polymer. Specifically, the content ofthe magnetic filler is preferably 100 to 450 parts by mass, morepreferably 100 to 300 parts by mass, and further preferably 120 to 250parts by mass, with respect to 100 parts by mass of liquid-crystallinepolymer. It is advantageous that the content of the magnetic filler withrespect to the liquid-crystalline polymer is within this range becausethe electromagnetic shielding effect and mold processing property arewell balanced. Note here that when a plurality of types of magneticfiller is used as the magnetic filler, the total amount is made to bewithin the above-mentioned range; and similarly, when a plurality oftypes of liquid-crystalline polymers are used, the total amount is madeto be within the above-mentioned range.

The liquid-crystalline polymer composition of the present invention canbe obtained by mixing the liquid-crystalline polymer and the magneticfiller by various well-known means, but it is preferable that theliquid-crystalline polymer composition is obtained by melt-kneading theliquid-crystalline polymer and the magnetic filler from the viewpoint oflow cost, and it is more preferable that it is obtained in a form ofpellets by melt-kneading extrusion.

A typical melt-kneading extruder used for melt-kneading extrusion isequipped with a cylinder having a heater, and a screw for extruding ahot melt into the cylinder; and it may be a single-screw kneadingextruder provided with one screw in a cylinder so that it is driven tobe rotated or may be a twin-screw kneading extruder provided with twoscrews in a cylinder so that they are driven to be rotated in thedifferent directions or in the same direction, but the use of thetwin-screw kneading extruder is advantageous for the liquid-crystallinepolymer composition of the present invention.

In the melt-kneading extruder, it is preferable that the ratio (L/D) ofthe effective length (L) of the screw to the diameter (D) of the screwis 20 or more (L and D are the same scale unit) because the magneticfiller is dispersed more uniformly in the liquid-crystalline polymer.Herein, the effective length of the screw denotes a length of the screwin the axial direction and the diameter of the screw denotes a nominalouter diameter dimension of the screw.

Furthermore, it is preferable that this melt-kneading extruder has aplurality of supply ports. In order to form a hot melt from theliquid-crystalline polymer and the magnetic filler and to obtain pelletsof the liquid-crystalline polymer composition of the present invention,firstly, to the melt-kneading extruder from an upstream-side supply portprovided in the upstream-side in the extrusion direction of themelt-kneading extruder, 50 mass % or more of the total supplied amountof the liquid-crystalline polymer is supplied and 50 mass % or less ofthe total supplied amount of the magnetic filler is supplied. Then, theremaining amount of the liquid-crystalline polymer ([the total suppliedamount of the liquid-crystalline polymer]−[the supplied amount of theliquid-crystalline polymer supplied from the upstream-side supply port])and the remaining amount of the magnetic filler ([the total suppliedamount of the magnetic filler]−[the supplied amount of the magneticfiller supplied from the upstream-side supply port]) are supplied to themelt-kneading extruder from the downstream-side supply port provided inthe downstream side in the extrusion direction than the upstream-sidesupply port. Thus, for the hot melt, a contact time between theliquid-crystalline polymer and the magnetic filler can be relativelyshort, and thus the deterioration of the liquid-crystalline polymertends to be suppressed, and therefore it is advantageous in productionof the liquid-crystalline polymer composition of the present invention.In this point, it is preferable that the supplied amount of theliquid-crystalline polymer from the upstream-side supply port is 60 mass% or more with respect to the total supplied amount. Furthermore, it ispreferable that the supplied amount of the magnetic filler from theupstream-side supply port is 20 mass % or less with respect to the totalsupplied amount. Note here that when the components other than theliquid-crystalline polymer and the magnetic filler as mentioned aboveare contained in the liquid-crystalline polymer composition of thepresent invention, such components are preferably supplied from thedownstream side supply port together with the magnetic filler.

Examples of the method of forming the thus obtained liquid-crystallinepolymer composition of the present invention include injection molding,extrusion molding, transfer molding, blow molding, press molding,injection press molding, and extrusion injection molding, and two ormore thereof may be employed in combination if necessary. Among them,for producing electric and electronic components used in electric andelectronic equipment, melt molding such as injection molding andextrusion injection molding is preferable and injection molding is morepreferable.

The injection molding can be carried out by melting theliquid-crystalline polymer composition of the present invention, heatingthe melted liquid-crystalline polymer composition to an appropriatetemperature, and injecting it into a mold having a desired cavity shapeby using an injection molding machine (for example, “HydraulicHorizontal Molding Machine PS40E5ASE” manufactured by Nissei PlasticIndustrial Co., Ltd.). The temperature at which the liquid-crystallinepolymer composition is heat and melted for injection is preferablyTp′+10 (° C.) or higher and Tp′+50 (° C.) or lower when the flowstarting temperature Tp′ (° C.) of the liquid-crystalline polymercomposition to be used is defined as a basic point. Furthermore, thetemperature of the mold is usually selected from the range between roomtemperature and 180 (° C.) from the viewpoint of the cooling rate andthe productivity of the liquid-crystalline polymer composition.

It is preferable that the thus obtained molded article has a volumeresistivity value of 10⁶ Ωm or more. Furthermore, the electromagneticshielding property is preferably 1 dB or more when it is expressed by anattenuation effect with respect to high frequency of 2.5 GHz.

It is preferable that the thus obtained molded article can be appliedfor various applications of use, and, in particular, it is preferablyused as surface mounting components by taking use of the electricinsulation property and the electromagnetic shielding property. Examplesof such surface mounting component include a housing, a choke coil, aconnector, and the like, of electric and electronic components. Themolded article formed by molding the liquid-crystalline polymercomposition of the present invention is used as surface mountingcomponents extremely advantageously because an effect of absorbing anelectromagnetic wave noise can be expected.

EXAMPLE Examples 1 to 5 and Comparative Example 1

[Production of Liquid-Crystalline Polymer] In a reactor equipped with astirring device, a torque meter, a nitrogen gas inlet tube, athermometer, and a reflux cooler, 994.5 g (7.2 moles) ofp-hydroxybenzoic acid, 446.9 g (2.4 moles) of 4,4′-dihydroxybiphenyl,299.0 g (1.8 moles) of terephthalic acid, 99.7 g (0.6 moles) ofisophthalic acid, and 1347.6 g (13.2 moles) of acetic anhydride werecharged; the inside of the reactor was fully replaced with nitrogen gas,the temperature was then raised to 150° C. over 30 minutes undernitrogen gas stream, and reflux was carried out for 3 hours with thetemperature kept. Then, the temperature was raised to 320° C. over 2hours and 50 minutes while distillate acetic acid generated as aby-product and unreacted acetic acid anhydride were distilled away; thecontent was extracted from the reactor at the time when the increase oftorque was observed, and the content was cooled to room temperature andthen pulverized into powder by using a coarse crusher. The temperatureof the powder was raised from room temperature to 250° C. over 1 hour ina nitrogen atmosphere, and raised from 250° C. to 285° C. over 5 hours,and kept at this temperature for 3 hours; thereby carrying out solidphase polymerization and then cooling thereof to obtain aliquid-crystalline polymer. The flow starting temperature of thisliquid-crystalline polymer was 327° C.

[Heat Treatment of Composite Material (Preparation of Magnetic Filler)]An electromagnetic wave absorption filler (manufactured by HitachiHigh-Technologies Corporation, volume average particle size: 20 μm,aspect ratio: 2.7) as a composite material formed by coating iron powderwith silica particles was charged in a crucible, which was placed in anelectric furnace, and heat-treated in a nitrogen atmosphere attemperatures and for periods of time shown in Table 1 so as to obtainmagnetic filler.

[Production and Molding of Liquid-Crystalline Polymer Composition] Aliquid-crystalline polymer and a magnetic filler were kneaded at theratio shown in Table 1 at 330° C. by using a unidirectional twin-screwextruder (“PCM-30HS” manufactured by Ikegai Iron Works Ltd.), extrudedinto strands at the rate of 10 kg/h, cut and granulated to obtain apellet-shaped liquid-crystalline polymer composition. At that time, 70mass % of the total supply amount of the liquid-crystalline polymer wassupplied from the upstream-side supply port of the extruder; and 30 mass% of the total supply amount of the liquid-crystalline polymer and thetotal amount of the magnetic filler were supplied from thedownstream-side supply port of the extruder. The obtainedliquid-crystalline polymer was subjected to injection molding at acylinder temperature of 340° C., a mold temperature of 130° C., and atthe injection rate of 30 cm³/s by using an injection molding machine(“PS40E5ASE” manufacture by Nissei Plastic Industrial Co., Ltd.) toobtain a molded article 1 (a molded article having a size of 64 mm×64mm×1 mm). Furthermore, similarly, the injection molding was carried outto obtain a molded article 2 (ASTM, dumbbell No. 4).

[Evaluation of Granulation Property] In the above-mentioned granulation,the number of occurrences of strand breakage during production of 1 kgof pellets was visually observed and evaluated according to thefollowing 3 stages, and results are shown in Table 1.

A: zero, B: 1 to 4 times, C: 5 times or more.

[Measurement of Electromagnetic Wave Attenuation Effect]

The molded article 1 was used and measurement was carried out atfrequency of 2.5 GHz by using a coaxial-tube type (“S-39D” manufacturedby Keycom Corporation) in conformity with ASTM D4935.

[Measurement of Volume Resistivity] The molded article 1 was used andmeasurement was carried out by using “SM-10E Super Insulation Meter”(manufactured by To a Denpa Kogyo K.K.), in conformity with ASTM D257.

[Measurement of Tensile Strength] The molded article 2 was used andmeasurement was carried out in conformity with ASTM D638.

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 4 Example 5Example 1 Liquid-crystalline 100 100 100 100 100 100 polymer (part bymass) Magnetic filler 150 150 150 150 230 150 (part by mass)Heat-treatment 800 900 900 900 900 Not temperature (° C.) heat-treatedHeat-treatment time (h)  20  5  12  20  20 Granulation property B B A AA C Electromagnetic wave   1.4   2.0   1.5   2.0   3.0   2.0 attenuationeffect (dB) 2.5 GHz Volume resistivity value   10¹³   10¹³   10¹³   10¹³  10¹³   10¹³ (Ωm) Tensile strength (MPa)  70  68  70  72  50  30

Examples 6 to 8 [Production and Molding of Liquid-Crystalline PolymerComposition]

A liquid-crystalline polymer and a magnetic filler were kneaded at theratio shown in Table 2 at 355° C. by using a unidirectional twin-screwextruder (“PCM-30HS” manufactured by Ikegai Iron Works Ltd.), extrudedinto strands at the rate of 15 kg/h, cut and granulated to obtain apellet-shaped liquid-crystalline polymer composition. At that time, 70mass % of the total supply amount of the liquid-crystalline polymer wassupplied from the upstream-side supply port of the extruder, and 30 mass% of the total supply amount of the liquid-crystalline polymer and thetotal amount of the magnetic filler were supplied from thedownstream-side supply port of the extruder. The obtainedliquid-crystalline polymer was subjected to injection molding at acylinder temperature of 340° C., a mold temperature of 130° C., and atthe injection rate of 30 cm³/s by using the injection molding machine(“PS40E5ASE” manufacture by Nissei Plastic Industrial Co., Ltd.) toobtain a molded article 1 (a molded article having a size of 64 mm×64mm×1 mm). Furthermore, similarly, the injection molding was carried outto obtain a molded article 2 (ASTM, dumbbell No. 4).

[Evaluation of Granulation Property] In the above-mentioned granulation,the number of occurrences of strand breakage during production of 1 kgof pellets was visually observed and evaluated according to thefollowing three stages, and results are shown in Table 2.

A: zero, B: 1 to 4 times, C: 5 times or more.

[Measurement of Electromagnetic Wave Attenuation Effect]

The molded article 1 was used and measurement was carried out atfrequency of 2.5 GHz by using a coaxial-tube type (“S-39D” manufacturedby Keycom Corporation) in conformity with ASTM D4935. Furthermore, themolded article 1 was used and measurement was carried out at frequencyof 10 GHz by using a coaxial-tube type (“S-GPC7” manufactured by KeycomCorporation) in conformity with ASTMD4935.

[Measurement of Volume Resistivity] The molded article 1 was used andmeasurement was carried out by using “SM-10E Super Insulation Meter”(manufactured by To a Denpa Kogyo K.K.), in conformity with ASTM D257.

[Measurement of Tensile Strength] The molded article 2 was used andmeasurement was carried out in conformity with ASTM D638.

TABLE 2 Example 6 Example 7 Example 8 Liquid-crystalline polymer 100 100  100  (part by mass) Magnetic filler 160  195  230  (part by mass)Heat-treatment temperature 900  900  900  (° C.) Heat-treatment time (h)18 18 18 Granulation property A A A Electromagnetic wave   1.5   2.1  2.9 attenuation effect (dB) 2.5 GHz Electromagnetic wave   5.7   6.1  8.0 attenuation effect (dB) 10 GHz Volume resistivity value  10¹³ 10¹³  10¹³ (Ωm) Tensile strength (MPa) 80 65 57

1. A liquid-crystalline polymer composition comprising: a liquid-crystalline polymer; and a magnetic filler formed by heat-treating a composite material of a ceramic powder and a soft magnetic metal powder in an inert gas atmosphere.
 2. The liquid-crystalline polymer composition according to claim 1, wherein the liquid-crystalline polymer is a fully aromatic liquid-crystalline polyester.
 3. The liquid-crystalline polymer composition according to claim 1, wherein the liquid-crystalline polymer has a repeating unit represented by formula (i), a repeating unit represented by formula (ii) and a repeating unit represented by formula (iii): —O—Ar¹—CO—  (i) —CO—Ar²—CO—  (ii) —O—Ar³—O—  (iii) wherein Ar¹ represents a 1,4-phenylene group, a 2,6-naphthalenediyl group or a 4,4′-biphenylylene group; Ar² and Ar³ each independently represent a 1,4-phenylene group, a 2,6-naphthalenediyl group, a 1,3-phenylene group or a 4,4′-biphenylylene group; and a hydrogen atom present in the group represented by Ar¹, Ar², or Ar³ may each independently be replaced by a halogen atom, an alkyl group or an aryl group.
 4. The liquid-crystalline polymer composition according to claim 1, wherein the ceramic powder contains silicon oxide as a main component.
 5. The liquid-crystalline polymer composition according to claim 1, wherein the soft magnetic metal powder contains iron or an iron alloy as a main component.
 6. The liquid-crystalline polymer composition according to claim 1, wherein an aspect ratio of the soft magnetic metal powder is 2 or more.
 7. The liquid-crystalline polymer composition according to claim 1, wherein the composite material is a composite material formed by coating the soft magnetic metal powder with the ceramic powder.
 8. The liquid-crystalline polymer composition according to claim 1, wherein the magnetic filler is a magnetic filler formed by heat-treating the composite material in the inert gas atmosphere at 800° C. or higher.
 9. The liquid-crystalline polymer composition according to claim 1, wherein the composite material is a composite material formed by coating the soft magnetic metal powder with the ceramic powder, and wherein the magnetic filler is a magnetic filler formed by heat-treating the composite material in the inert gas atmosphere at 800° C. or higher.
 10. The liquid-crystalline polymer composition according to claim 1, wherein a content of the magnetic filler is 100 to 450 parts by mass with respect to 100 parts by mass of the liquid-crystalline polymer.
 11. The liquid-crystalline polymer composition according to claim 1, obtained by: supplying the liquid-crystalline polymer and the magnetic filler to a melt-kneading extruder equipped with a screw having a ratio (L/D) of an effective length (L) of the screw to a diameter (D) of the screw of 20 or more, a first supply port, and a second supply port provided in a downstream side of the first supply port in an extrusion direction, such that 50 mass % or more of the total supply amount of the liquid-crystalline polymer and 50 mass % or less of the total supply amount of the magnetic filler are supplied from the first supply port and a remaining portion of the liquid-crystalline polymer and a remaining portion of the magnetic filler are supplied from the second supply port; and melt-kneading the supplied materials.
 12. A molded article formed by molding the liquid-crystalline polymer composition according to claim
 1. 13. The molded article according to claim 12, wherein a volume resistivity value is 10⁶ Ωm or more, and an attenuation effect with respect to an electromagnetic wave at frequency 2.5 GHz is 1 dB or more. 